Added toString() methods to UnionSplit, SeededSplit and CartesianSplit to

ensure that the proper keys will be generated when they cached.

src/scala/spark/RDD.scala

@@ -165,7 +165,10 @@ extends RDD[Array[T]](prev.sparkContext) {
 }
 
 
-@serializable class SeededSplit(val prev: Split, val seed: Int) extends Split {}
+@serializable class SeededSplit(val prev: Split, val seed: Int) extends Split {
+  override def toString() =
+    "SeededSplit(" + prev.toString + ", seed " + seed + ")"
+}
 
 class SampledRDD[T: ClassManifest](
   prev: RDD[T], withReplacement: Boolean, frac: Double, seed: Int) 
@@ -268,6 +271,7 @@ private object CachedRDD {
 abstract class UnionSplit[T: ClassManifest] extends Split {
   def iterator(): Iterator[T]
   def preferredLocations(): Seq[String]
+  def toString(): String
 }
 
 @serializable
@@ -276,6 +280,8 @@ class UnionSplitImpl[T: ClassManifest](
 extends UnionSplit[T] {
   override def iterator() = rdd.iterator(split)
   override def preferredLocations() = rdd.preferredLocations(split)
+  override def toString() =
+    "UnionSplitImpl(" + split.toString + ")"
 }
 
 @serializable
@@ -297,7 +303,10 @@ extends RDD[T](sc) {
     s.asInstanceOf[UnionSplit[T]].preferredLocations()
 }
 
-@serializable class CartesianSplit(val s1: Split, val s2: Split) extends Split
+@serializable class CartesianSplit(val s1: Split, val s2: Split) extends Split {
+  override def toString() =
+    "CartesianSplit(" + s1.toString + ", " + s2.toString + ")"
+}
 
 @serializable
 class CartesianRDD[T: ClassManifest, U:ClassManifest](